



L 


»* III 0 


^ 1 


IN THE WEST. 


BY 




T. F.GLESTON, Ph.D., 

b 

NEW YORK CITY. 


A Paper Read before the American Institute of Mining 
Engineers, at the Roanoke (Va.) Meeting, June, 1883. 






AUTHOR’S EDITION. 
1 8 8 3 . 




















































































•r> 

cA 

[TRANSACTIONS OF THE AMERICAN INSTITUTE OF MINING ENGINEERS . 1 



V 

A 


<5 

LEACHING GOLD AND SILVEE GEES IN THE WEST 

BY THOMAS EGLESTOX, PH.D., NEW YORK CITY, 
i Read at the Roanoke (Va.) Meeting, June. 1883.» 

The process of lixiviating silver ores, which do or do not contain 
gold, by means of hyposulphite of soda is likely to assume a very 
great importance in the West, the conditions being such that while 
it is applicable to very rich ores which do not contain lead enough 
to smelt, it is also equally applicable to many ores that are either 
too poor or too impure to be treated by any other process. Western 
ores are generally divided into four classes: those which contain 
copper enough to be smelted for copper from which the gold and 
silver is extracted in the wet way, as is the practice of the Boston 
and Colorado works; those in which there is a large quantity of 
lead, which can be smelted for lead, and the gold and silver ex¬ 
tracted from it; ores in which there is neither copper nor lead 
enough to allow of a process of smelting, but which can be treated 
•in pans, these ores being “free milling” if they require no metal¬ 
lurgical treatment, or “rebellious ” if they have to be roasted with 
or without the addition of salt ; and ores which do not contain 
enough either of lead or copper for smelting, which are poor both 
in silver and gold, contain large amounts of sulphur, arsenic, and 
antimony, and cannot be treated in many places in the West by any 
of these processes. Roasting with salt would convert the base metals 
as well as the silver into chlorides, and would give in the amalga¬ 
mation a very base bullion, and the expense of the process would be 
so great that the margin of profit would be very small, the reason 
being that for the ordinary process of pan amalgamation, which is 
the only one suitable for ores containing small amounts of the base 
metals, and poor in silver and gold, the cost of a plant for milling 
is so large as not to justify the expense of treating such ores. The 
electrolytic processes which have been partially successful in Europe 
have not been tried here. While in the near future thev will un- 
doubtedly be used, it is hardly possible to consider them now. 

1 


2 


LEACHING GOLD AND SILVER ORES IN THE WEST. 


They can only be used near great centres of population, or where 
the amount of ore to be treated is so very large that it would justify 
a very expensive plant. When the trial period is passed this method 
will undoubtedly be applicable to many ores whose treatment is not 
now even discussed as possible. There are very large quantities of 
low-grade ores containing about thirty ounces of silver, with little 
or no gold, to the ton which might be treated if a not very expensive 
plant could be used. 

The process of leaching with the hyposulphites of soda or lime has 
not attracted much attention in the West as yet, partly because im¬ 
perfect experiments made with it in a small way have not been suc¬ 
cessful. It has also been thought that, while the price of salt is very 
low in these regions, it would be impossible to use any amount of a 
reagent which was high-priced like hyposulphite of soda. As far as 
the chemicals are concerned, while the price of salt is very low, all 
the salt, in any process where it is used, is lost. This expense is, 
therefore, a considerable one when very large quantities of ore are 
treated; and though the price of hyposulphite of soda is high, the 
amount consumed is extremely small, since all but a very small portion 
of the liquid is saved, as most of it is regenerated and used over again. 
There are very few places in the West where lime cannot be had. 
The use of sulphide of calcium, which is so easily made as a precip¬ 
itating reagent, makes it quite possible to use the leaching process, 
as this gradually transforms the hyposulphite of soda into hypo¬ 
sulphite of lime, the use of which has a great advantage in the treat¬ 
ment of ores containing even a very small quantity of gold, as the 
hyposulphite of lime dissolves nearly the whole of the gold, and al¬ 
lows of its being extracted while the hyposulphite of soda does not. 
The quantity of water used with pan amalgamation must always be 
at a maximum, even though it is used over again.* The quantity 
used with hyposulphite leaching is always a minimum, since all the 
water used in the process can be used over and over again, even the 
washing water being serviceable, so that the loss of water will be 
very small. In addition to this the plant which is to be used is a 
very cheap one, being composed of roasting furnaces, which need 
not be of a very expensive type, of wooden tubs, of not very costly 
materials, and requiring for the most part only low-priced labor. 
The process, however, requires careful watching by an expert, and 
continual assays, in order to see that there is no waste of silver nor 
of the reagent. 


Engineering, vol. xvii., p. 516. 


it: 

jM.llvi. 



* 









LEACHING GOLD AND SILVER ORES IN THE WEST. 


3 


Besides this, the California practice invariably associates with the 
pan the California stamp, which has always been considered one of the 
best machines for crushing, In the case of surface ores, however, 
especially such as contain silver, either in a native state or as 
chlorides or bromides, or where they contain sulphide of silver, the 
stamp is a very bad machine, because it tends to beat out the pieces 
so thin that they float, or in case of brittle ores to make flour, and in 
this way permits of their being carried off by the water. Later Eu¬ 
ropean practice shows that this has such an effect in enriching the tails 
that rolls are there gradually taking the place of stamps. The rolls 
simply crush or disintegrate the material, and are much less expen¬ 
sive than the stamps. But even supposing the stamps to be replaced 
by rolls, the rest of the amalgamation plant—the furnaces, pans, 
and settlers—is costly, requires constant repair, and must, in a period 
more or less short, wear out and be replaced. The mercury is, too, 
an expensive and troublesome reagent. The consequence is that 
the capital required for a leaching plant is very much less than it 
would be in a milling one. The leaching process is also applicable 
to ores containing both gold and silver, for when hyposulphite of 
soda is used after the ores have been leached for silver, the tails can 
be treated by Plattner’s process, and the gold and the silver both re¬ 
covered in a state of high bullion, so that a parting process would 
not be necessary, and when hyposulphite of lime is used they are re¬ 
covered together. It is also applicable to ores very rich in silver as 
well as to very poor ores, whether they are or are not very impure 
or are contaminated with other metals, since, when it is worth while 
to do so, small amounts of copper, cobalt and nickel may be sepa¬ 
rated.* There is, however, a limit to the quantity of base metals, 
especially lead, which can be treated. This wall depend in every 
case on the quantity of silver and on the cost of reagents. It is 
never applicable to ores which contain lead enough to smelt. 

In some cases where the ores were very rich in pyrites but poor 
in gold and silver, a matte concentration has been made and the ex¬ 
traction done on the roasted matte. Such an application necessitates a 
a cheap fuel, but the concentration can be carried on so as to materially 
reduce the amount to be treated. In Mexicof this process has been 
used on the amalgamation tails, containing large quantities of lead 
and 0.24 per cent, of silver. 

It is not, however, to be supposed that the process has no disad- 


* Annales des Mines, 5 Series, No. 8, p. 68. 

f Zeitschrift for das Berg-Hiitten und Salinen-Wesen, vol. xxi. (1873), p. 143. 


f 





J 


4 LEACHING GOLD AND SILVER ORES IN THE WEST. 


vantages. While the plant is very inexpensive, it requires careful 
attention on the part of those in control of it, for although the re¬ 
actions are exceedingly delicate they can be learned by men of very 
ordinary capacity, provided they are properly superintended ; but 
the least carelessness on their part, either in the roasting, leaching or 
precipitation, or by adding too much or too little of the reagent, in¬ 
volves very serious losses. 

The process has assumed some importance of late from its use at 
the Old Telegraph and Lexington mills, the works at Triumfo, in 
Lower California, and from the erection of a large plant recently at 
the Geddes and Bertrand mine in Secret Canon near Eureka, Nevada, 


where a poor ore full of impurities is treated. 

I have thought that 

a description of the process as used in these 

localities would be of 

interest. I have therefore described no mill 
most of the details refer to the Bertrand mill. 

in particular, though 

The analysis of the ore from the Bertrand mine is given below: 

Silicic acid,. 

. 50.25 

Iron, ....... f 

. 8.06 

Zinc, ........ 

. 7.62 

Lead,. 

. 4.64 

Arsenic,. 

. 0.73 

Antimony,. 

. 1.35 

Silver,*. 

. 0.17 

Lime,. 

. 4.92 

Magnesia,. 

. 2.40 

Sulphur, ........ 

. 0.96 

Carbonic acid, ....... 

. 8.30 

Water,. 

. * . 3.80 

Loss and Oxygen, ...... 

. 6.80 

Alumina, ........ 

trace 

Bismuth, ........ 

U 

Copper,. 

it 

Potassium, ....... 

it 

Sodium, ........ 

it 


100.00 


The process consists of seven different operations : 

1. Crushing the ore. 

2. Drying the ore. 

3. Roasting it with salt. 

4. Leaching out the base metals with water. 

5. Leaching with hyposulphite of soda. 

6. Precipitating the silver. 

7. Roasting the sulphide of silver and melting for bullion. 


* About $50 per ton. Most of the ore is, however, of a lower grade than this. 


















LEACHING GOLD AND SILVER ORES IN THE WEST. 5 


1. Crushing the Ore. 

The ore of the Bertrand mine comes from a higher level than the 
mill. It is brought in wagons drawn by horses and is dumped into 
a tunnel leading to the mill, falling through a shoot into cars on a 
track running into the highest level of the mill. Eventually a tun¬ 
nel will be run directly to the mine, which is about a fourth of a 
mile distant, and the ore will come to the mill without previously 
discharging. 

From the cars the material is dumped upon a grizzly, which is 
an inclined iron grating allowing only the small pieces to pass, and 
sending the large ones directly into a crusher, which after breaking 
them up discharges them into the same bin into which the small 
pieces which passed through the grizzly have fallen. From this 
bin the ore falls through a shoot into cars which carry it to the 
driers. In some works the large pieces pass through two sets of 
crushers, and what passes through the grizzly goes into a second 
crusher set fine, into which all the ore which does not pass the 
screens also falls. The ore is crushed so as to pass a 15 to 20 mesh 
screen. 30 mesh screens were first used, but it was found that the 
material did not discharge from these as well as from a coarser 
mesh, and that there was no necessity of treating the ore finer, as 
the roasting and leaching were better done on the coarse ore. 
Experience has shown that with the coarse screens more ore 
can be treated in a given time, as it leaches faster and there 
is less fine material to clog the filter. With fine ore it sometimes 
takes six or seven days to leach, and even then it is imperfectly done. 
In making an examination of the effect of coarse and fine screens 
it was found that in using those with from 20 to 40 meshes, 31 per 
cent, of the ore passed through ; from 40 to 60 mesh screens, 14 per 
cent.; from 60 to 80 mesh screens, 6 per cent.; and finer than this 
scarcely an appreciable quantity passed, without mechanical agita¬ 
tion such as comes from the blow of the stamp or the agitation of 
the screen. The size adapted to each ore can only be determined 
by experience, as ores which are apparently the same act differently 
in leaching. The only general rule that can be given is that the ore 
must be crushed just as coarse as is consistent with perfect chlorura- 
tion* in the furnace, which can easily be determined by trial. This 
question has received but little attention. It has more importance 

* The word chloruration is used to describe the formation of chlorides by means 
of salt, in contradistinction to chlorination, used to describe the formation of chlo¬ 
rides by means'of chlorinejgas. J 








6 LEACHING GOLD AND SILVER ORES IN THE WEST. 


than is generally attributed to it, and when improperly done easily 
translates itself into both a diminished output and a loss of money. 

The ore, wet before passing through the driers, assayed Septem¬ 
ber 28th, 1882, $26.71 ; on September 29th the assay was $29.85, 
and on the 30th, $23.85. These assays were taken from a large car 
into which a sample from every mine car is thrown. The mean of 
these three is $26.80, which is a little low, the net assays being 
about $30. They are given because the other assays are made on 
charges made the same day. 

2. Drying the Ore. 

The ore is damp when it comes from the mine and is taken from 
the crusher to the driers. These are revolving wrought-iron cylin¬ 
ders, 20 feet long by 4 feet in diameter at one end and 8 feet at the 
other, known under the name of Pacific driers. The iron work for 
the driers weighs about ten tons; they are not lined. The flame from 
the fireplace runs directly through them, the ore being fed at one end 
automatically by the Hendley’s Challenge Automatic Feeder, and 
dumped out into cars at the other end of the drier, without manipu¬ 
lation. These driers are usually heated by a fireplace of their own, 
which, however, is not absolutely necessary, as the flames from the 
Bruckner’s cylinders might be made to pass through them and then 
be made to pass into the dust chambers, thus utilizing a large amount 
of waste heat. When only small samples of ore are to be treated 
they are carried to a special bin, and put through a Dodge Crusher, 
which is used almost exclusively for sampling. Drying-floors, made 
by passing the waste heat through flues covered with cast iron plates, 
are used in some works. This saves the fuel used in the driers; but 
this economy is more than compensated for by the labor required, 
the driers being automatic in their action. 

After the ore leaves the drier it is carried to a bin from which it 
passes over a 15-mesh screen, and falls through a shoot in which is 
arranged a system of magnets to catch any pieces of metal which 
may have accidentally got into the ore, either in the mine or in the 
mill, such as bits of broken picks or drills, as they would be likely 
to injure the rolls, if they were allowed to pass through them. 
The ore then passes through two sets of Krom rolls, 16 by 24 
inches, from which, all that passes through the screens is carried by 
a chain elevator to a storage bin in the upper part of the building. 
What fails to pass the screens is carried back and put through the 


LEACHING GOLD AND SILVER ORES IN THE WEST. 


7 


rolls again. The ore from the rolls assayed on September 28th, 
1882, $27.75 ; on September 29th, $25.13, and on the 30th, $24.19. 

3. Roasting the Ore with Salt. 

From the storage bin the ore descends through a shoot into cars 
standing on a track scale, where it is weighed. The contents of the 
cars are dumped into a hopper above the Bruckner’s cylinders, the 
amount of each charge passing into the hopper being carefully 
weighed. The moment the hopper is discharged into the cylinder 
beneath another charge is put in. The salt is not weighed. It is 
measured in soap boxes which contain about 80 pounds each, and is 
mixed with the ore either in the driers or in the hoppers; formerly 
five per cent, of the weight was mixed with the ore. This amount 
was gradually decreased until now only three per cent, is used. 

A number of experiments have been made as to the best place to 
add the salt. Formerly it was always added in the hoppers, and 
became thoroughly mixed by the movement in the cylinders. Now 
it is added in the driers, and by incorporation resulting from the 
movement there and in the rolls it has been found that the quantity 
of salt may be considerably reduced, so that they now do not use 
more than a third of the salt they formerly did. Very extensive ex¬ 
periments have been made in Europe on the best place to add the salt 
in the various metallurgical works where salt is used for the extrac¬ 
tion of the metal, which has resulted in the adoption of a very 
ingenious mixing machine, into which the ore and salt are charged, 
which has produced great economy in the use of salt and better subse¬ 
quent working. Both methods are successful, but the introduction 
in the drier seems the best, as it takes the place of the mixer in the 
European methods. At first two per cent, of iron pyrites was mixed 
with the ore in order to insure a proper roasting. The quantity was 
diminished little by little until now none is used. In most cases, how¬ 
ever, where there is a large amount of base metals this addition will 
be necessary. 

All the conveying of the ore is done with chain elevators having 
pockets 6 by 4 inches. These are used for the dry ore only, the 
chloridized ore is not elevated. Repairs to these chain elevators are 
very easy, for when a link is broken it has only to be taken out and 
another one put in, or if for anv reason it is desirable to make the 
chain shorter or longer the links can be readily removed or added. 

The ore is now ready to be roasted. This may be done in any 
kind of a furnace. Where transportation is difficult a reverberatory 


8 


LEACHING GOLD AND SILVER ORES IN THE WEST. 


furnace, with a hearth arranged in three steps, so that the ore in 
passing from one to the other falls a distance of 4 to 5 feet, would be 
the best. A Stetef'eldt furnace could also be used to advantage. The 
iron work, as it is in pieces of no very great weight, can be easily 
transported, but is more expensive to build than a reverberatory 
furnace, which can always be easily adapted to any kind of fuel. 
At the Bertrand mill, which is within easy reach of San Fran¬ 
cisco by railroad, there are four Bruckner’s cylinders, which are 
7 feet in diameter and 19 feet long, and hold a charge of about live 
tons. The fireplace is on a prolongation of the axis of the furnace, 
but was formerly put at right angles to it, greatly to the inconve¬ 
nience of the workmen. The cylinder is driven by friction rollers, 
of which there are three sets, and not by a gear-wheel round the 
body of the cylinder as in the older form. The work is continuous, 
the furnace never being allowed to become cool. As soon as a 
charge has been treated a fresh charge is immediately put in. To 
introduce the charge the man-hole is brought under the hopper and 
its valve drawn. It is then replaced and the cylinder set to revolving 
two to three turns per minute. The amount of sulphur contained 
in the Bertrand ores is exceedingly small, so that the salt in very 
small quantity, if it has not already been added in the driers, may be 
introduced at once. When ores containing a large amount of sulphur 
are used, a careful roasting at a low temperature must precede the 
chloruration, steam at a low pressure being introduced for the pur¬ 
pose not only of getting rid of the last trace of sulphur, arsenic, 
and antimony,* but also to decompose the chlorides of the volatile 
base metals, the nascent chlorine thus given off acting very ener¬ 
getically on the silver. When the ore contains base metals which 
it is desirable to save,f this roasting must be done with great care, 
and the value of the base metals separated must compensate for the 
extra expense in fuel owing to the use of steam in the roasting. If 
lead is present, the roasting must be done at a low temperature, for 
as the compounds of lead are easily fusible, there might be danger 
of agglomeration; or, if the temperature is high and silica is present 
also, a silicate of lead might be formed which would prevent the 
solution of the silver. Special care must be taken in such a case to 
transform all the lead into chloride, as this is soluble in hot water, 
while the sulphate is not. 

The roasting lasts eight to eleven hours, depending on how the 


* Engineering, vol. x'xii., p. 515. 
f Annales des Mines, 5 s., vol. viii., p. 70. 



LEACHING GOLD AND SILVER ORES IN THE WEST. 


9 


charge works. When it is finished the man-hole is opened without 
stopping the cylinder, which in its rotation discharges the ore, which 
falls into pits cut out of the rock in the foundation, just underneath the 
cylinders, where it is allowed to remain about nine hours, until it is 
ready to go to the cooling floor. These pits have been found to be a 
very great advantage, for it has been ascertained that a considerable 
amount of chloruration takes place in the* pit after the charge 
leaves the furnace, so that the time of waiting is not lost. It is 
red hot when it falls into the pits, but cools sufficiently to be drawn 
off into cars after that time. Occasionally the ore, when for any 
reason there is a stoppage, remains for two or three days in this 
bin and is still hot when drawn. Generally, however, it is drawn 
out on the cooling floor as soon as possible, where it is at once 
moistened with water to keep down the dust. Sometimes the ore is 
put into the tub so hot that the water boils, but this is not usual. 
The ore is generally cold enough not to make any appreciable dif¬ 
ference in the temperature of the water. When the ore is one which 
is not habitually treated, a sample is drawn through the fireplace 
in order to test the chloruration. When, however, the ore is that 
which they are constantly using, they recognize that it is finished 
by its rolling about in the furnace with a sluggish motion somewhat 
like that of damp sugar. 

When the furnace is discharging two assay samples are taken from 
every charge. When about half the charge of the furnace has run out 
a long iron spoon is run underneath and filled and its contents assayed. 
One of these samples is used for a chloruration test, which is made at 
once for each charge, each assay sample being marked with the 
number of the charge and of the furnace or the cylinder; the other 
is thrown into a large iron car to be afterwards used in making the 
general assay to ascertain the amount of silver contained in the ore. 

The following table gives eleven assays of the ores taken from 
each of the furnaces during different days: 

ASSAYS.* 


No. of charge. 

No. of furnace. 

Value. 

74 

1 

$25.44 

75 

1 

30.16 

81 

3 

32.36 

81f 

3 

31.42 


* I am indebted for these and the following assays to my pupil, Mr. C. F. Pearis, 
who was for some months assayer at the Bertrand mill, 
f After remaining two days in the bin. 





10 


LEACHING GOLD AND SILVER ORES IN THE WEST. 


No. of charge. 

No. of furnace. 

Value. 

84 

9 

mt 

28.27 

85 

3 

33.30 

86 

3 

27.96 

115 

4 

30.16 

116 

4 

27.96 

117 

4 

25.75 

118 

9 

4 

27.33 


Occasionally the charge of ore from the furnace is more than the 
tub will hold. This residue is put into a heap, and when enough 
of it has accumulated to fill a tub it is leached and called a “ mixed 
charge.” 

On September 28th, 1882, the ore from the cylinder assayed 
$32.99 ; on September 29th, $30.47; on September 30th, $27.96. 
These assays on the same charges and days are interesting, and are 
given below together. 



Sept. 28. 

Sept. 29. 

Sept. 30. 

Damp mine sample, 

26.71 

29.85 

23.88 

Sample from the rolls, 

27.65 

25.13 

24.19 

“ “ Bruckner’s cylinder, . 

32.99 

30.47 

27.96 

« u u « 

32.36 

• • • 

30.32 


The assay for chloruration is made on the sample taken from the 
charge. Fifteen ounces are weighed out and put into a funnel with 
a proper filter. Hyposulphite from a tank above is let on to it and 
allowed to run from fifteen to twenty minutes, the filtrate being col¬ 
lected and sent to the leaching tubs. When no silver is dissolved 
the assay is washed and dried, and a fusion assay made of the tails. 
Twenty-three such assays are given in the table below. 


CHLORURATION ASSAYS. 


No. of 

No. of 


No. of 

No. of 


charge. 

furnace.. 

Value. 

charge. 

furnace. 

Value. 

81 

3 

$5.49 

Ill 

2 

$3.92 

81* 

3 

5.20 

112 

2 

3.61 

101 

1 

5.18 

113 

2 

3.77 

102 

1 

4.40 

114 

2 

4.24 

103 

1 

2.98 

184 

4 

3.29 

104 

• 

1 

4.40 

185 

4 

4.08 

105 

1 

3.77 

186 

4 

3.14 

106 

1 

4.71 

187 

4 

3.45 

107 

1 

3.14 

188 

4 

3.45 

108 

2 

3.77 

190 

4 

4.55 

109 

2 

3.45 

198 

4 

3.29 

110 

2 

3.61 





* After remaining two days in the bin. 






LEACHING GOLD AND SILVER ORES IN THE WEST. 


11 


The following tables give the details of 24 charges in the cylin¬ 
ders during a period of six days. They give a complete record of 
the work of the furnace during that time. The corresponding 
table for the tubs, and also the chloruration and tub-tailing assays, 
are given on pages 19 and 20. These tables comprise the details of 
the entire work of the mill for four days. 


Number 
of furnace. 

Number of 
charge. 

Ore. 

Salt, lbs. 

Pyrites, 
per cent. 

Cars of 
flue-dust. 

Hours 

roasting. 

Tons. 

Lbs. 


Mixed charge. 

5 


450 

2 



2 

67 

5 

532 

720 

2 

3 

10 


Mixed charge. 

5 


450 

2 



2 

68 

7 


720 

2 



2 

69 

7 

803 

720* 

2 


8 


Mixed charge. 

5 


450 

2 



2 

70 

7 

1041 

720 

2 

4 

11 

2 

71 

5 


720 

2 

3 

934 1 

2 

72 

6 

1758 

480 

2 

5 

9 % 

2 

73 

7 

50 

720 

2 


8 % 

3 

74 

7 

140 

700 

2 


13 

3 

75 

5 

600 

480 

2 


1 % 

4 

88 

5 

1642 

640 

2 

2 

7M 

4 

94 

7 

440 

720 

2 


10 

4 

95 

6 

1116 

720 

2 

1 

8 % 

4 

96 

5 

1835 

720 

2 

2 

8 % 

4 

97 

7 

140 

720 

2 


10 

f 4 

98 

4 

134 

720 

2 

3 

93^ 

4 

99 

7 


720 

2 


1034 

4 

100 

3 

667 

640 

2 


934 

4 

101 

7 

1800 

720 

2 


9?J 

4 

102 

7 

220 

720 

2 




Mixed charge. 

5 


450 

2 



| 

Mixed charge. 

5 


450 

2 




The Bruckner’s cylinders are run by an upright engine with a 
cylinder 10 by 12 inches. 

When the ore in the collecting-bins is sufficiently cool, it is drawn 
into cars and taken to a brick cooling-floor, where it is dampened 
with water and spread out with hoes. The collecting-bins are 12 feet 
deep and extend from the bottom of the cylinders to the top of the 
car on the floor below. The works are built on the side of a hill, 
which is a very convenient arrangement. No attempt is made to 
keep ore ahead. It is the intention to have two charges on the cool¬ 
ing-floor and one charge in each of the furnaces and a charge in each 
of the hoppers. The roasting is done bv two men on each shift, each 
man tending two cylinders, with two Chinamen bringing the wood 
which is used as fuel. 

All the machinery other than the Bruckner’s cylinders is run by 

an engine with a 14-inch cylinder with a 48-inch stroke, which is 

much larger than is required for the work. 12 cords of wood are 

burned in the 4 Bruckner’s cylinders in 24 hours. The wood is 

•/ 

cedar, nut-pjne and mountain-mahogany, which are all excellent 








































12 


LEACHTNG GOLD AND SILVER ORES IN THE WEST. 


woods. They are equal to or even better than the lignites which are 
the usual fuels of the country, judging them by weight. The driers 
burn three cords of wood per day, the engine four, the stoves to heat 
the leaching-room one. 20 cords of wood are used for the 24 hours 
for the entire work of the mill. 

One engineer on each shift runs the boilers and the engine. Pie 
is a Chinaman and has one helper, who is also a Chinaman. 

A considerable amount of chloride of silver and of dust contain¬ 
ing silver is volatilized or mechanically carried off from both the 
Bruckner’s cylinders and the driers. It is, therefore, necessary to 
have dust-chambers connecting with both of these. The flues have a 
down-take, which communicates with a large chamber by an arched 
opening, which is quite small. The dust accumulates in considera¬ 
ble quantities at the bottom of the down-take, so that they are 
obliged to clean it frequently. This material and that which comes 
from the dust-chambers is collected. It is then passed through the 
Bruckner cylinders and mixed with the charges as shown in the table, 
p. 11. Fresh salt is added to it and it is put through the tubs. 
Sometimes, when large quantities are on hand, it is treated sepa¬ 
rately. 

4. Leaching the Base Metals with Water. 

The leaching-room contains 24 tubs, 12 on a side, each of which 
is six feet in diameter and three feet deep, the depth being regulated 
according to the facility with which the water will filter through 
the ore, and also to the ease with which a man can throw out the 
tails. It would be much better to increase the diameter of the tubs 
to twelve feet; it is done in many of the works in Lower California 
and Mexico, the depth being the same as here. Experience in 
these countries has shown that a better result is obtained with large 
than with small tubs. These tubs are set on the floor together in 
pairs, the two tubs almost touching each other, with a railway upon 
one side and an easy passage-way between each pair of tubs. The 
track runs close to the side of the tubs. That the discharging may 
be done with facility, the wagon which receives the tails comes just 
above the top of the tubs, so that a man standing in them can 
easily throw the tails out into the wagon. 

Permanently fixed above the tubs are hoppers, which are long 
and narrow. They are divided into two compartments, and have at 
their bottom a slit-valve, so that the ore may be discharged from each 
compartment in little piles over all parts of the bottom of the tub. 
Each tub may have its own hopper, made of iron, as at the Bertrand 


LEACHING GOLD AND SILVER ORES IN THE WEST. 


13 


mill, or one hopper may answer for two or more tubs, the discharge 
being made by flexible pipes. Stop-cocks or plugs do not answer 
for the leaching tubs, as they are apt both to get out of order and 
to leak. A rubber pipe can always be securely fastened to the bot¬ 
tom or side of the tub* and when not in use can be hung up out of 
the way. The ore is passed from the cooling-floor to the vats as 
rapidly as it can be handled, each charge of ore being drawn from 
the furnace-bins to the cooling-floor as soon as the latter is empty. 
The cars from the cooling-floor run over the top of the hoppers and 
dump their contents into them, which from there fall into the tubs 
when the si it-valve is opened, and the ore is afterwards evenly dis¬ 
tributed over the bottom of the tub with a hoe. The charge could 
as easily be put into the tubs from a car running on a railroad at a 
sufficient height above the tub not to inconvenience the workmen 
in discharging it, and arranged with a valve like the hopper, or it 
could be dumped into the vat from the side. 

The bottom of the tubs is covered with four or five wooden slats, 
three inches by one, which do not touch the sides. Over these, at 
right angles, are arranged other slats from an inch to an inch and a 
half apart. Gunny-sacking, which is wet from the previous charge, 
or is wet purposely when a new filter is to be put in, is placed 
over these. It is brought close up against the sides of the vat, so 
that no ore will pass, by means of a hoop, which fastens it securely 
there. The ore falls from the hopper upon this canvas and rises to 
within two or three inches of the top of the tub. When the ore is* 
once in the tub, special care is taken that it shall not be disturbed in 
any way. Once ready for the water it is allowed to remain without 
being disturbed until the tails are ready to be discharged. Any in¬ 
terference with the arrangement in the tub increases the difficulty 
of leaching. The simple pushing of a stick two or three times 
down through the ore may delay the leaching several hours. 

In the bottom of the tub are two india-rubber pipes, about 1J 
inches in diameter, one for introducing the water and the other for 
discharging it. When hot water is used for leaching out the base 
metals the ore is always wet from the bottom, the water being in¬ 
troduced through the pipe and coming up through the ore. It has 
been found that this method of moistening the charge causes the ore 
to cake less and the solutions to percolate through them much more 
easily than when the water was introduced from above. As soon as 
the water completely covers the ore the supply is cut off. After re¬ 
maining there for a very short time, the discharge-pipe, which has 


14 LEACHING GOLD AND SILVER ORES IN THE WEST. 

up to this time been hung up higher than the top of the tub, is 
lowered and the water allowed to run out; the leaching water is added 
at the same time. This water is permitted to flow away entirely or 
is collected, according to the quantity of water available. The water 
used for the base-metal leaching may be hot or cold. If the ore con¬ 
tains a large amount of lead which has been converted into chloride 
it will be best to leach with cold water until the larger part of the 
lead and the surplus salt has been dissolved out. It is then leached 
with hot water, cooling the ore, however, with cold water before 
the hyposulphite is added, in order to prevent too great an extrac¬ 
tion of the base metals with the silver. When the ore filters slowly 
it will be found best to heat the water, which will not onlv make it 
filter more easily, but will dissolve the base metals more rapidly. 
When the charge comes warm from the cooling-floor, when intro¬ 
duced into the tub, the water grows warm from the heat. In such 
a case, unless the ores are very pure, or where very impure ores have 
been leached with hot water, the charge must be cooled with cold 
water before introducing the hyposulphite, or the bullion would be 
much more impure. 

As the water introduced from the bottom subsides, a very thin 
crust is formed upon the top of the charge, which is carefully re¬ 
moved and put by itself until sufficient accumulates to be treated. 
This material is quite rich in silver. It contains all the silver which 
was dissolved bv the excess of salt or other chlorides in the ore, and 
. which would have been lost if the hot water had been introduced at 
the top. This amount is all the larger if the solutions are hot, or 
if the excess of salt is large, as a hot brine dissolves more silver 
according as it is hot and saturated, while a cold one dissolves 
hardly any. The dilution of the liquor with water precipitates part 
of the silver near the top and distributes the rest of it through the 
ore, so that but little is lost in bottom leaching. The top crust is 
collected in barrels : there is but a small quantity on each tub, but, 
as there are 24 tubs constantlv in use, it amounts to considerable bv 
the end of the month. After this has been removed clear cold water 
is allowed to run in at the top, the quantity being regulated so that 
the inflowing water will just be equal to the quantity discharged, in 
order to leach out the base chlorides which are soluble. Any salt 
in excess, or any which has not been decomposed in the roasting, 
will be dissolved at the same time. When the ore contains but little 
base metal there is no advantage in using hot water. This is the 
case at Triumfo, in Lower California, where the ore is always 
leached cold and the water introduced from the top. 


LEACHING GOLD AND SILVER ORES IN THE WEST. 


15 


When the ore, however, contains a great excess of lead or anti¬ 
mony, the method of introducing the water from below is not suffi¬ 
cient, as the chlorides of these metals also are precipitated from the 
solution by dilution with water. In such a case the water is intro¬ 
duced from the top and the liquid allowed to flow from several 
tanks into compartments filled with shavings, so as to get a large 
amount of surface. Clear water is allowed to How into these com¬ 
partments, so as to make the liquor very dilute. The moment the 
fresh water touches the stream containing the chlorides, which was 
formerly clear, it becomes cloudy, and then precipitates the chlorides. 
Flowing over so large a surface, and being obliged to pass under one 
compartment and over the other, the chlorides of silver, lead and anti¬ 
mony deposit on the shavings, and can be dissolved from them with 
hyposulphite and the solution put with the other silver solutions. 
The water running off contains the zinc, copper and iron. At 
Triumfo the ore contains four per cent, antimony and but little 
lead. No attention is paid to the antimony, the ores being leached 
with cold water. In Mexico the washing is repeated, the ore being 
discharged from the first tub to be put into a second. The first 
washing lasts for four hours and the second a little less ; the observa¬ 
tion having been made that even when no metal salts are found in 
the wash-water of the first washing some are found in that of the 
second; and only when nothing is precipitated from the second 
washing is the leaching with hyposulphite begun. In the West but 
one washing is generally made. 

When the water flowing from the tubs no longer gives a precipi¬ 
tate when tested with sulphide of calcium, the base-metal chlorides 
are removed. When there is plenty of water, as at certain seasons 
of the year, all of this water is allowed to run to waste, if the ore 
contains no nickel or cobalt or other metals which are worth collect¬ 
ing. When, however, the water is scarce, or the base metals are 
valuable, it is all collected in the vats. The base-metal chlorides 
are precipitated with sulphide of calcium and the water used over 
again. It takes a quantity of water equivalent to three tubfuls 
to leach the base-metal chlorides out. 

5. Leaching with Hyposulphite of Soda. 

The washed ore is now leached with a cold solution of hyposul¬ 
phite of soda. The strength of the solution will depend on the rich¬ 
ness of the ore and the quantity of base metals present. If the ore 


16 


LEACHING GOLD AND SILVER ORES IN THE WEST. 


is very rich and but little base metal is present it may be used very 
strong, and even warm; but when base metals are present too much 
of them would be extracted, so that the solution is usually made 
weak and used cold. At Triumfo the quantity used is generally 
one pound to eight gallons of water. At the Bertrand mill it con¬ 
tains from half to three-fourths of a pound to the gallon. The 
hyposulphite is usually purchased. It comes to the works in small 
kegs, containing from 50 to 60 pounds each, and does not usually 
cost more than five to six cents a pound. It is generally cheaper to 
purchase it than to make it. The liquors increase in quantity as 
the solutions are constantly being regenerated, so that but small 
additions have to be made, and this only to keep up the strength 
of the solution, as the liquors are constantly being diluted. The 
hyposulphite is likely to become impure when the ores are not 
properly leached with water to dissolve out the sulphate of soda 
and chloride of sodium ; it is generally the practice then to regen¬ 
erate it by spreading wood ashes over the ore and leaching through 
that, the alkalies in the ashes taking up the sulphates and the ex¬ 
cess of chlorides. By the constant use of the polysulphide of cal¬ 
cium it gradually becomes converted into hyposulphite of lime. It 
is sometimes desirable, especially when the ore contains gold, to use 
hyposulphite of lime, especially as the polysulphide of calcium 
which is used for the precipitation of the silver is the first step in 
the process of manufacturing it. This is done by boiling 1.5 parts 
of the purest freshly slacked lime that can be had with one part of 
crushed brimstone. Flowers of sulphur sifted through a fine sieve is 
also used, but it does not answer so well as the brimstone, which can 
be more readily obtained and is more easily manipulated. If the 
lime is not very pure it may be desirable to use two parts of lime to 
one of sulphur. When sulphur is scarce and high-priced it is some¬ 
times collected from roasting the sulphide of silver. The water is 
first boiled with steam, the lime is added and well stirred, and the 
sulphur is then introduced. Sufficient water must be added to keep 
the mass liquid, but not enough to allow of the solution of polysul¬ 
phide becoming too much diluted. The boiling is kept up from three 
to four hours. During this time polysulphide of lime, mixed with 
hyposulphite of lime, is formed, as shown by the formula below: 

3CaO + 12S = 2CaS 5 + CaS 2 O s . 

This operation requires some care. If lime is added in excess 
insoluble compounds are apt to form. Sometimes bisulphide of lime 


LEACHING GOLD AND SILVER ORES IN THE WEST. 


17 


is formed, which crystallizes out as reddish-yellow crystals. An 
excess ot sulphur, however, does no harm, and may be useful 
in the next operation. The liquid is allowed to settle and the 
clear liquid decanted. It is desirable that this solution should 
be from 8° to 10° Baume, and only sufficient water is added 

to bring it up to that strength. The liquid is now treated with 

sulphurous acid, made by boiling charcoal broken to about the size 
of a grain of corn, with sulphuric acid of about 1.80° B., enough 
being used to make a pasty mass. This is done in an iron retort, 

adding the acid to the charcoal as it is necessary. There is no ne¬ 

cessity ot purifying the gas. When the yellow color of the liquid 
disappears the sulphide has been converted into hyposulphite. This 
is tested with a dilute solution of chloride of silver. So long as 
there is any precipitate or cloudiness the passage of the sulphurous 
acid must be continued ; when there is none the solution is ready. 
The residue in the tub is now treated with the same amount of 
water as before, and the operation commenced over again. If the 
resulting liquor is not more than 3° to 4° B., it is too weak, and is 
kept to treat the next charge of lime. The process used at Triumfo 
is much simpler. The residues left in the tub after the clear sulphide 
liquid is decanted are simply shovelled out and left for three or four- 
days exposed to the sun. They are then leached with water, which 
extracts the hyposulphite of lime, after which they are thrown away. 
This method is a very rough one, as the oxidation is necessarily very 
imperfect, but for that situation is a much more economical method 
than the use of sulphurous acid. 

The sulphide of calcium made in the first stage of the process is 
the material used for precipitation. It should not be less than 6° B. 
if used for that purpose. In some works the poly sulphide of sodium, 
made by boiling soda with sulphur and treating it with sulphurous 
acid to make hyposulphite of soda, is used. This reagent does 
not precipitate the silver so rapidly, nor so well, and is not so 
easily washed. For this reason the hyposulphite of lime is preferred. 
Sometimes sulphuretted hydrogen, made by melting paraffine and 
fiowers of sulphur together, is used for the precipitation. This is 
much more disagreeable than the other method and is not so fre¬ 
quently used. Where hyposulphite of soda is used, the constant 
addition of lime transforms the solution gradually into hyposulphite 
of lime. The strength of this solution is constantly kept up with a 
hydrometer. 

When the ore is very impure, it is generally best to keep the so- 

3 


18 LEACHING GOLD AND SILVER ORES IN THE WEST. 

lution at about Baume. Before turning the solution into the 
precipitating vats, care must be taken to see that the water used for 
leaching out the base metals has been displaced. This is easily done 
by tasting, as the hyposulphite of soda and silver has an intensely 
sweet taste, or better by testing the liquor flowing from the tanks 
with sulphide of calcium. As soon as the least turbidity is shown, 
it is time to catch the liquor, as the hyposulphite is acting. This 
hyposulphite liquor is allowed to run through as long as it has a 
sweetish taste. No special attention is paid to the time at the Ber¬ 
trand mill, as the work is done by Chinamen whose records would 
not be very intelligible or trustworthy ; tests only are relied on. The 
reaction which takes place is 

2AgCl T 2Na 2 S 2 0 3 -f 5H 2 0 = 2NaCl + 2NaAgS 2 O s -f 5H 2 0. 

This hyposulphite of soda and silver is exceedingly soluble. The 
quantity of hyposulphite, and also the time required for leaching, will 
depend on the richness of the ore, more time being required for a 
rich than for a poor one. Ores are rarely treated that require a 
longer time than twenty to thirty hours. An ore containing from 
$300 to $400 a ton, will be perfectly leached in twelve to fifteen 
hours. The time required at the Bertrand mill is from six to 
twenty hours, depending on the ease with which the hyposulphite 
filters. 

As soon as the hyposulphite ceases to taste sweet, the solution is 
tested with sulphide of calcium to ascertain whether the ore is ex¬ 
hausted of silver. The tester carries a small bottle of the sulphide 
solution in which he has a stick. He takes a tumblerful of the 
liquid running out and lets a drop or two of the sulphide fall into 
the liquor in the glass. If there is a precipitation of sulphide of 
silver, the lixiviation is continued. If there is no precipitate, and 
the liquor becomes only slightly discolored, he puts in some of the 
liquor containing the silver solution to ascertain whether there is an 
excess of sulphide of calcium. In this case the hyposulphite solu¬ 
tion is discontinued and the excess of hyposulphite must be 
washed out with cold water. The exhaustion of the hyposulphite 
is distinguished by the taste. This last liquor, as it contains nothing, 
goes to the fresh-water tanks. 

It takes from 18 to 48 hours to charge, leach, and discharge the 
ore, the time depending on the way the roasting has been done. Ex¬ 
ceptionally a charge will take a longer time, sometimes as much as 
five or six days. In Mexico the leach liquor is divided into two 


LEACHING GOLD AND SILVER ORES IN THE WEST. 


19 


parts, as it has been found that that coming off first contains much 
less of the sub-sulphates and oxychlorides of the base metals than the 
last, and consequently produces a purer bullion. This is not done 
in the West, and, when all the product must be cupelled with lead, 
is not necessary. 

The following table gives 37 assays of the tub tailings made at the 
Bertrand mill during four days. They show a very low value in 
silver. 


Tub Tail Assays from August 28 th to Septem¬ 
ber 1st, 1882. 


No. of charge. 

No. of furnace. 

No. of tub. 

Value. 

76 

2 

7 

S3.14 

81 

3 

4 

6.59 

87 

2 

17 

4.87 

89 

2 

2 

4.71 

90 

2 

5 

4.71 

92 

2 

24 

4.55 

94 

4 

14 

4.08 

98 

4 

2 

3.14 

99 

4 

4 

4.08 

101 

4 

8 

4.08 

103 

2 

2 

3.92 

104 

2 

6 

4.08 

105 

4 

1 

3.61 

106 

4 

14 

3.92 

107 

2 

11 

4.08 

108 

4 

6 

3.77 

109 

2 

16 

3.29 

110 

2 

6 

4.71 

132 

3 

19 

3.61 

135 

3 

3 

4.40 

138 

3 

15 

5.18 

140 

3 

1 

1.08 

141 

3 

7 

4.24 

143 

3 

14 

3.92 

144 

8 

21 

4.08 

146 

3 

9 

4.24 

147. 

3 

17 

4.24 

148 

3 

3 

3.92 

150 

3 

21 

4.08 

172 

4 

4 

4.40 

173 

4 

8 

4.87 

174 

4 

12 

3.45 

175 

4 

22 

3.29 

176 

4 

20 

4.55 

178 

4 

10 

4.55 

180 

4 

5 

4.55 

183 

4 

20 

3.29 


As soon as the water ceases to flow, a probe sample is taken from 
three points in each tub, and they are sent to the assay office to see 
whether there is any silver left. The ore assays from 30 to 50 ounces ; 
the tails should assay only about 4 ounces. These assays are being 
constantly made, 20 to 30 being often made in a day. If the assays 
show that the silver is down to from 4 to fi ounces, the tub is dis¬ 
charged, if not, the ore has to be re-roasted and treated with the 
hyposulphite again. This rarely happens, however, for, as the 














20 LEACHING GOLD AND SILVER ORES IN THE WEST. 

assays are constantly being made, the exact condition of the ore is 
known before the leaching commences. 

The ore from the tubs is shovelled into cars and run out to the 
dump-heap at the rear end of the mill, where there is a turn-table 
to switch the cars into the proper track. Care has to be taken at 
first to see that the men do not cut the gunny-sacking in shovelling 
out the ore. At first, before the men are experienced, it is generally 
considered a necessary precaution to cover the gunny-sacking with 
slats from five to six inches apart, to insure that it is not cut by the 
shovels. When, however, the workmen are experienced, they know 
when they are near the bottom from the height to which they have 
to throw the leached ore, and they are so careful not to dig on the 
sacking that these slats need not be used. The sacking is very sel¬ 
dom cut after the men are accustomed to the work. 


The following table gives the details of the leaching of the same 
charges, the details of which, during the roasting process, are given 
on page 11. 


, No. of 
'furnace 

No. of charge. 

Hours on 
water. 

Hours on 
soda. 

Total hrs. 
leaching. 

Assay. 

Chlorin¬ 

ation. 

Ttib tail¬ 
ings. 

NO. of 
tub. 


Mixed charge. 

n% 

4934 

61 

25.44 

4.08 

4.71 

1 

2 

67 

9| 

19 

28 f 

42.73 

3.45 

3.67 

16 

17 


Mixed charge. 

11 % 

2514 

37 % 

28.89 

8.79 

4.24 

2 

68 

1134 

17 

28% 

46.18 

6.12 

3.92 

19 

2 

69 

10 

15)4 

25% 

27.65 

5.18 

3.98 

23 


Mixed charge. 

1034 

2034 

30f 

44.49 

6.59 

4.87 

24 

2 

70 

13 

29 

42 

27.33 ' 

3.45 

3.61 

3 

2 

71 

10 % 

2734 

38 

31.42 

7.38 

5.18 

5 

2 

72 

io% 

17 

2734 

26.07 

6.41 

5.49 

7 

2 

73 

6 

23 

29 

27.02 

3.61 

3.92 

9 

3 

74 

9 

15 

24 

29.52 

6.28 

3.87 

22 

3 

75 

10 

7 

17 

26.71 

4.40 

6.28 

21 

4 

88 

9 

20 

29 

31.72 

2.03 

6.28 

15 

4 

94 

lot 

19 

29 1 

32.99 

3.61 

4.08 

14 

4 

95 

1434 

98 

112% 

35.19 

9.66 

6;12 

13 

4 

96 

6 * 

12 

18* 

44.49 

2.98 

3.67 

18 

4 

97 

8 

534 

13*4 

29.85 

6.12 

4.24 

20 

4 

98 

1134 

2734 

39 

25.75 

4.40 

3.14 

2 

4 

99 


16 

25% 

31.42 

4.08 

4.08 

4 

4 

100 

9 

sy 

17% 

27.96 

4.01 

3.61 

6 

4 

101 

6 Vi 

uy 

21 

25.13 

3.92 

4.08 

8 

4 

102 

18 % 

27 % 

46% 

29.21 

6.91 

3.77 

10 


Mixed charge. 

6 

32 

38 

45.25 

6.59 

4.87 

11 


Mixed charge. 

1934 

6634 

86 

26.71 

4.08 

5.34 

12 


Just as soon as the tub is empty a fresh charge is put in. The 
24 tubs are kept constantly working. Three men have entire charge 
of the tubs; they only work during the daytime. The leaching, 
however, is continuous, and is done by two Chinamen on each shift. 
They fill all the tubs, do all the testing and take the probe samples. 
No other persons are allowed to touch the tubs while they are under 
their care. When the leaching is finished three laborers discharge 
the tubs, and carry the tails to the dump-heap. The head leacher 
is paid $2.50 and his helper from $1.00 to $1.50 per day. Fifty or 
sixty tons a day are leached by these two men. 







































LEACHING GOLD AND SILVER ORES IN THE WEST. 


21 


6. Precipitation of the Silver. 

The hyposulphite liquor containing the silver is run directly from 
the leaching vats to the precipitating tanks, which are 8 feet in di¬ 
ameter and 12 feet deep. All the solutions, except the silver liquors, 
are carried about the mill through wooden launders, carefully jointed, 
with tar, and also painted on the inside with it. This is an excellent 
method. Iron pipes were formerly used, but they decomposed the 
solutions and sometimes precipitated the silver. Iron pipes lined 
with tar would be a better arrangement, especially in those mills 
whose work is not continuous. These might be ordinary steam- 
pipes, five inches in diameter, which are screwed together. Wooden 
troughs without the coating of tar were formerly used, but it was 
found almost impossible to keep them tight, and the penetrating 
nature of the hyposulphite caused a considerable loss of the reagents. 
Besides, when not used they shrank, which was a very great disad¬ 
vantage, as they leak for some time afterwards. Troughs hollowed 
out of solid wood are used in some works, but they are not easily 
made and are more difficult to manage. The whole of this incon¬ 
venience, however, is remedied by the use of iron pipes lined with 
tar. 

The silver liquors from all the leaching tubs are run into one pre¬ 
cipitation vat until it is filled to within 15 to 20 inches of the top, 
the flow is then turned into the next vat. When this is done, the sil¬ 
ver is thrown down at once, sulphide of calcium being added until no 
precipitation takes place. The solution is then agitated for some 
minutes to make a thorough mixture, and is then allowed to settle, 
and the clear liquor which is reconverted into hyposulphite of lime 
and soda by the sulphide of calcium is drawn off into a receiving 
tank on a lower level, and from there forced into a tank on the top 
floor, from which all the solution used runs. The reaction which 
takes place is 

2XaAgSA + 2NaCl + 10H 2 G + CaS = Ag 2 S 4- 2.Na 2 S 2 0 3 -f - 

CaCl 2 + 10H 2 O. 

This solution in Mexico is at 25° to 30° Beaume, in the West it is 
much weaker. 

Where various ores are treated, it requires a little time to ascer¬ 
tain just the quantity of sulphide to add, but when the same ores 
are constantly being used, it is simply measured in from a pail. 
There is no danger of loss, as the liquors are carefully tested. Care 
must be taken not to have the sulphide in excess. Only that por¬ 
tion of the sulphide which precipitates the silver is converted into 


22 


LEACHING GOLD AND SILVER ORES IN THE WEST. 


hyposulphite of lime; any excess of sulphide would cause a precipi¬ 
tation of the silver already dissolved in the solution-tanks as sul¬ 
phide, which would not be dissolved by the hyposulphite and would 
consequently be lost in the tails. If there is an excess of sulphide 
some of the silver liquor must lie added to neutralize it. At the 
Bertrand mill the sulphide of calcium added in the precipitation of 
the silver keeps the liquor up sufficiently with the weekly addition 
of about fifty pounds of hyposulphite. As soon as the clear liquors 
are run off other liquors are run in and precipitated, clarified and 
so on, for about two weeks. At the end of that time the tanks must 
be discharged. There are three precipitating tubs for the sulphide 
of silver and three for the precipitation of the base metals with the 
same sulphide when water is scarce. 

A great deal of trouble has been experienced in the various works 
in pumping these solutions. In this mill an ordinary Babcock’s 
steam-pump was used, but iron pumps were found not to work well, 
and steam pressure was then used to force the liquors up, which had 
a great many inconveniences. The simplest way is that formerly 
used at the Old Telegraph mine, which was to use an ordinary lift¬ 
ing pump made with a wooden cylinder lined with hard rubber, with 
a hard-rubber plunger, which cost less than $50. This pump worked 
perfectly for a long time without repairs. 

Every fifteen days the sulphide of silver is collected. The ar¬ 
rangement is made to have the whole mill cleaned up at one time. 
To do this the sulphide in the bottom of the tanks is stirred vigor¬ 
ously until the material is in the state of a thin mud. It is then drawn 
off from the bottom of the tank and run over cloth filters. These 
filters consist of a series of frames about 2J feet square, over which 
sacking is securely fastened. There are 30 of these frames, 3 in a 
row, built on the same table, which is surrounded by a rim 3 inches 
high. Underneath the table is an inclined trough which carries all 
the liquors to the collecting vat. The turbid liquor from the pre¬ 
cipitating vat is run on to this table and flows from one sacking to 
the other. The solution drains through and the pasty sulphide re¬ 
mains on the sacking. This operation is constantly repeated until 
the sulphide of silver has accumulated in considerable quantity on 
the sacking. It is then washed with clear water to remove the ex¬ 
cess of sulphide of calcium until it is perfectly sweet. It is then left 
to dry. In drying:, it cracks in every direction. It is shovelled 
into a car and carried to the reverberatory furnace to dry and roast. 

J J 

As there is a considerable amount of water in the pasty mass, it is 


LEACHING GOLD AND SILVER ORES IN THE WEST. 


23 


in some works collected in canvas bags and the water squeezed out 
with a press before it goes to the furnace. 

7. Roasting the Sulphide of Silver and Melting 

for Bullion. 

The sulphide of silver is now ready to be dried in a reverberatory 
furnace, as it still contains some water. The heat must be quite low 
at first, only just enough being used to burn off the sulphur. It 
can only be increased very slowly at first for fear of melting the 
sulphides. It is roasted until most of the sulphur is driven off, and 
the heat is then raised to as high a temperature as possible without 
melting. When sulphur is scarce the sulphide is heated in a retort, 
and the sulphur condensed to be used over again. Mr. O. H. Aaron 
proposes to take the freshly precipitated sulphide and boil it, adding 
freshly slacked lime in small quantities at a time to the liquor, which 
is kept constantly agitated. When this is carefully done the poly- 
sulphide of calcium will be formed much more quickly than by the 
direct action of the sulphur, and most of the sulphur in the sulphide 
of silver will be regained. The liquor is decanted, and the residue 
is dried and roasted. After roasting, it is a gray mass composed 
almost entirelv of metallic silver. 

Formerly the roasted silver was melted in graphite crucibles, but 
this was found to be too expensive. It is now cupelled with the ad¬ 
dition of lead in an English cupel. The litharges are rich in silver 
and are all reduced to form the lead for the next cupellation. From 

X 

the cupels it is cast into bricks and is between 800 and 900 fine. 
No attempt is made to make it finer, as it is found cheaper to sell 
it than it is to refine it. 

It must not be taken for granted that the bullion produced from 
this process is necessarily purer than that produced by any other. 
The contrary is likely to be true. If the ore contains a large quan¬ 
tity of base metals, particularly lead, these would be only partially 
affected by amalgamation, while most of the lead contained in the ore 
will be likely to be found in the bullion made by leaching. The reason 
for this is that while all that portion of the lead which is in the form 
of chloride may be leached out, and, by the judicious arrangement de¬ 
scribed, the other metals can be separated, none of the lead present 
as sulphate will be attacked by the water, while most of it will be 
dissolved by the hyposulphite and will be precipitated by the sul¬ 
phide, thus using a larger amount of the reagent, and being a direct 
source of loss. This, however, except in very poor ores, is not a 
grave inconvenience. In other respects the bullion is likely to be 


24 LEACHING GOLD AND SILVER ORES IN THE WEST. 

i 

purer. The loss is practically very small. The outlay for chemicals 
is also very small, as they are constantly regenerated, and the same 
water can be used over and over again. The amount of necessary 
loss in the tails will depend, other things being equal, on the price ot 
labor. It is very easy to ascertain this by making a daily clean up, 
or making a time assay, to ascertain exactly how much is being ex¬ 
tracted in a given time. The assay shows that 85 per cent, of the 
silver in the chloridized ore is saved. From 50 to 60 tons are easily 
treated in the twenty-four hours. The average product of the Ber¬ 
trand mill is from $30,000 to $40,000 per month ; that of the Tri- 
umfo works is from $50,000 to $60,000 per month. 

There are 60 men in all employed in the Bertrand mill. The 
following table gives the special occupation of each of these men and 
the wages they receive. 

/ 

MEN REQUIRED TO RUN THE BERTRAND MILL DURING 

24 HOURS. 


Roasters—furnace men, 

. 2 


n 

00 

$8 

00 

—feeders, 

. 2 

@ 

3 

00 

6 

00 

Driers and rollers, 

. 10 

@ 

3 

00 

30 

00 

Cooling-floor, 

. 6 

@ 

3 

00 

18 

00 

Leaching-floor, Chinamen, . 

. 2 

@ 

2 

50 

5 

00 

H U << 

. 3 

@ 

1 

50 

4 

50 

Rock breakers, 

. 2 

@ 

3 

00 

6 

00 

Flue cleaners, 

. 4 

@ 

1 

50 

6 

00 

Blacksmith, 

. 1 

@ 

6 

00 

6 

00 

helper, 

. 1 

@ 

3 

00 

3 

00 

Carpenters, .... 

. 2 

@ 

5 

00 

10 

00 

Engineer, .... 

. 1 

@ 

5 

00 

5 

00 

U 

. 1 

@ 

4 

00 

4 

00 

Fireman, .... 

. 1 

@ 

2 

50 

2 

50 

Assayer, .... 

. 1 

@ 

5 

00 

5 

00 

Lamp cleaner, 

. 1 

@ 

1 

50 

1 

50 

Foreman, .... 

. 1 

@ 

6 

00 

6 

00 

ii 

. 1 

@ 

5 

00 

5 

00 

Office helper, 

. 1 

@ 

1 

50 

1 

50 

General helper, 

. 1 

@ 

3 

00 

3 

00 

Watchman, .... 

, 1 

@ 

3 

00 

3 

00 

Woodmen, Chinamen, . 

. 3 

@ 

1 

50 

4 

50 

<< «( 

4 

. 1 

@ 

3 

00 

3 

00 






$146 

50 


All the charging and discharging and leaching is done by four 
Chinamen and three Irishmen. The total cost of milling the ore 
is $6.50 per ton. The cost of mining and delivering the ore at the 
mill is about $2.50, which makes the total cost about $9.00 per ton 
of actual expense on each ton of 30 ounce ore. 



























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